1. Field of the Invention
This invention relates to a reactive component mixing apparatus and method for mixing the reactive components with filler. In one of its aspects, it relates to metering a dry filler into a reactive plural component mixture. In another of its aspects, the invention relates to a mixing head for dispensing a reactive mixture of components blended with a dry filler.
2. Description of Related Art
In many applications for polyurethane materials and other similar reactive components both cellular and noncellular it has been found beneficial to incorporate a dry filler material into the liquid polyurethane components. Examples of other reactive components include polyesters, epoxies, silicone, alkyd, acrylics and the like. Examples of filler materials include butane filled beads, solid or foam scrap regrind, global fiberglass, sand or melamine. Dry fillers such as melamine have a tendency to agglomerate which, if not broken up, could result in an inconsistent dispersion of the dry filler throughout the hardened polyurethane. This condition can create varying properties throughout the resulting polyurethane article.
Apparatuses have been developed to mix dry fillers with liquid polyurethane components. Examples of such mixing apparatuses are disclosed in U.S. Pat. No. 4,275,033, issued Jun. 23, 1981 to Schulte et al. and U.S. Pat. No. 3,920,233, issued Nov. 18, 1975 to Krueger. In each of these apparatuses, dry filler is supplied to a mixing head by rotating feed screws. The dry filler is then mixed with the liquid components by a mixing screw mounted on the same shaft as the feed screw.
U.S. Pat. No. 3,843,100 issued Oct. 22, 1974 to Haas et al. shows a polyurethane mixing head which combines a dry filler with the previously mixed liquid components. The filler and liquid components are mixed by a plurality of vanes and flights mounted to a rotating shaft within the mixing chamber.
U.S. Pat. No. 4,481,308 to Gray incorporates a screw conveyor to introduce urea into a mixing head for combination with the liquid polyurethane components. The mixing head incorporates a mixing screw to mix the urea and the previously mixed liquid components.
One problem which each of these mixing heads suffers from is the ability to accurately vary the amount of dry filler introduced into the mixing chamber in relation to the conditions as they presently exist within the mixing chamber. Another problem is that air is frequently entrapped within the dry filler and can cause air bubbles in the hardened product. Further some of the dry fillers such as butane filled beads are crushed if exposed to high shear forces. None of the prior dry filler polyurethane mixing heads appear to effectively eliminate entrained air from the mixing head. In addition, none of the dry filler mixing heads allow independent control of the mixing speed versus the feed rate.